This invention pertains to a switchable clamp-type locking mechanism. In this type of clamp-type locking mechanism, an output shaft is locked against rotating in either rotational direction with respect to a rotatably fixed part, in particular a housing, when a rotational moment is introduced to the output shaft. These types of clamp-type locking mechanisms often provide a drive means that transmits a rotational moment to the output means so that elements that are connected to the output shaft can be activated. In the transfer of rotational moment from the drive to the output means, the clamped connection between the output shaft and the rotatably fixed part is released in the selected direction of rotation. Switchable clamp-type locking mechanisms can, for example, be used in gear units that have an output shaft fixed in both rotational directions when a rotational moment is introduced to this output shaft. Such gear units are, for example, used in automobile seat adjustment systems or in devices to raise or lower windows in automobiles. In these cases, a rotational moment introduced from the outside to the output shaft, i.e. the load imposed on the seat by a person, for example, is taken up by a housing, for example, so that no rotational motion of the output means occurs.
From WO 96/20352 A, for example, a clamp-type locking mechanism is known that is provided in a seat height adjustment system. The clamp-type locking mechanism has two self-enclosed elements, the outer element of which is designed as a housing having a cylindrical track on its interior wall surface and the other element of which is designed as an output shaft whose external surface facing the cylindrical track is provided with a number of locking ramps with opposite slopes distributed along the perimeter. Each locking ramp forms a wedge-shaped clamping gap with the cylindrical track. A spring force pushes clamping rollers into this clamping gap. Since the virtual peaks of these wedge-shaped clamping gaps either face toward or away from one another, the clamping rollers that are pushed by a spring force into-the clamping gap prevent a rotational motion of the inner element with respect to the outer element in both rotational directions. The clamping rollers are pushed by a spring force into the clamping gap in their clamped position and engage with the locking ramps and the cylindrical track. When the clamping rollers are freed, i.e. when they are located in the released position, only those clamping rollers that are functionally relevant to this rotational direction are freed. The clamping rollers are located in the pocket of a cage with play in the perimeter direction, wherein the cage can be tilted with respect to the inner element just a bit. This tilting path is used to free the clamping rollers from their associated clamping gaps. A rotational moment acts on the inner element, which is caused by a force acting on the seat. In the clamped position, these types of clamp-type locking mechanisms hold the seat in its adjusted height.
Now, it is conceivable that not only static rotational moments can act on these types of clamp-type locking mechanisms in their clamped position, but also oscillating, dynamic loads with alternating rotational moments. If these types of clamping mechanisms are provided in automobiles, for example in seat adjustment systems, vibrations in the internal combustion engine can generate these types of loads. In an alternating load of this type, for example, the clamping force of the above clamp-type locking mechanism that is transmitted from the inner element to the outer element through the clamping rolls in their clamped position is first reduced until the alternating load reaches a value at least approaching zero. The rotational moment imposed between the working shaft and the housing can be reduced under this oscillating load to approximately 18 Nm or less. In this situation, of course, the clamping rollers are still being pushed by the spring force into their clamping gaps by means of the springs provided, but relative shifts are possible here between the inner element and the outer element due to the reduced clamping effect under the alternating load. As a result, an undesired slip can occur. In case of the seat height adjustment system, these types of relative shifts can result in the seat height undergoing an unwanted change.
The object of this invention is thus to securely prevent a slip between the clamped elements in switchable clamp-type locking mechanisms.
According to the invention, this object is met in that a slide that is fixed to the output shaft is form-locked to the rotatably fixed part in the clamped position of the clamping elements and disengages with the rotatably fixed part in the released position of the clamping elements. In the clamped position of the clamping elements, a rotational moment can be introduced to the output shaft and can be transferred through the clamping elements to the rotatably fixed part. In addition to this, a form-locked connection between the output means and the housing exists to prevent an undesired slip, as a result of oscillations, between the output means and the rotatably fixed part, for example the housing. The form-locked connection can be designed for small loads since most of the load is transmitted through the clamp-type locking mechanism and not through the form-locked connection between the output means and the housing. In case of oscillating or alternating loads that approach zero or pass through this value, the form-locked connection will be subjected to these minimum dynamic loads, preferably where zero is crossed. Of course, the form-locked connection can be designed to withstand maximum occurring rotational moments.
In a clamp-type locking mechanism according to the invention, the housing can be provided with a cylindrical track on its inner perimeter and the output shaft can be provided with the locking ramps on its outer perimeter. It is also possible to design the output shaft as a hollow shaft and to design the locking ramps into the inner perimeter of the hollow shaft and to design the cylindrical track at the outer perimeter of a part of the axis of the housing. Furthermore, it is possible for the locking ramps to be designed at the back of the output shaft and for the flat, circular closed track to be designed at the back of the housing. In any case, the track associated with the housing is flat in the sense that it is either flat or has a smooth bend.
A further development according to the invention provides that a mechanism is located between the drive shaft and the slide to convert a rotational motion of the drive shaft into a longitudinal shift of the slide. The rotational motion of the drive shaft is thus first used to release the form-locked connection between the slide and the housing by shifting the slide. The continued rotational motion of the drive shaft is transmitted to the output shaft.
Another further development according to the invention provides that a ramp is provided at the slide and an attachment for the ramp is provided at the drive shaft and at a distance from the rotating axis of the drive shaft. As the drive shaft rotates, the attachment B for example a pin located coaxial to the drive shaft B is turned in the circumferential direction. Since the slide is initially locked to the housing, it cannot follow the turning of the pin in the circumferential direction, resulting in the pin pressing up against the ramp. Under the force of the pin pushing against the ramp, the slide, which can shift lengthwise, now is forced to shift because the rampxe2x80x94and thus the slidexe2x80x94slides along the pin until the slide finally is disengaged from the housing. Then, the continued rotation of the drive shaft can be transmitted to the output shaft. The slope of the ramp determines the length of the path of the slide relative to the amount of the rotational angle of the drive shaft.
The slide can be made to move parallel to the output shaft. In this case, the ramp is provided at the back of the slide. The slide can also be made to move perpendicular to the output shaft. In this case, the ramp is tilted at an angle to the axis along which the slide is shifted. The virtual extension of the ramp then intersects the axis at an angle that determines the ratio between the distance that the slide shifts relative to the rotational angle of the output shaft. Two ramps with opposite slopes can cooperate with the attachment on the drive shaft. This has the advantage in that the slide can be shifted in a common longitudinal direction in both rotational directions of the drive shaft so as to release the form-locked connection between the output shaft and the housing. The ramp can also be provided at the output shaft and the attachment can be provided at the slide. This type of arrangement provides the same advantages described since this case is just the reverse arrangement of ramp and attachment.
Another further development according to the invention provides that the radially moving slide is provided with a triangular cut-out perpendicular to the drive shaft, wherein two abutting walls in the triangular cut-out each form one ramp. The virtual extensions of the ramps intersect the axis along which the slide moves. It is preferred that the ramps intersect this axis at the angle so that these virtual extensions intersect this axis at a common point. As a result, a radial movement of the slide is forced to occur in a common direction from both rotational directions of the drive shaft as has already been described in detail above.
In an advantageous manner, the clamp-type locking mechanism according to the invention can be provided with a spring so that moving the slide to release the form-locked connection occurs against the force of this spring. The advantage in this is that the slide automatically springs back under the return force of the spring and produces a form-locked connection between the output shaft and the housing if no rotational moment is introduced to the drive shaft.
The form-locked connection can, for example, be produced by providing teeth on both the slide and the housing, with the teeth engaging into each other to produce the form-locked connection. The smaller the distance between teeth, the more positions are available for the slide to produce the form-locked connection.